Cellular swelling is the first manifestation of almost all forms of injury to cells. It is a difficult morphologic change to appreciate with the light microscope; it may be more apparent at the level of the whole organ.

When it affects many cells in an organ, it causes some pallor, increased turgor, and increase in weight of the organ. On microscopic examination, small clear vacuoles may be seen within the cytoplasm; these represent distended and pinched-off segments of the endoplasmic reticulum. This pattern of nonlethal injury is sometimes called hydropic change or vacuolar degeneration. Swelling of cells is reversible.

The ultrastructural changes of reversible cell injury include:
 plasma membrane alterations

• blebbing
• blunting
• distortion of microvilli

 creation of myelin figures
 loosening of intercellular attachments
 mitochondrial changes

• mitochondrial swelling
• mitochondrial rarefaction
• appearance of small phospholipid-rich amorphous densities

 dilation of the endoplasmic reticulum

• detachment
• disaggregation of polysomes nuclear alterations
• disaggregation of granular and fibrillar elements

Example

 hepatocyte swelling